expected: |
  1,a,1,xxx,1,a
  2,b,,,2,b
  3,c,3,yyy,3,c
query: |
  -- Join from subquery.
  select t1.num, t1.name, t2.num, t2.value, t3.num, t3.name
  from 'Table1.csv' as t1
    left join (select * from 'Table2.csv') AS t2 ON t1.num = t2.num
    inner join 'Table1.csv' as t3 on t1.num=t3.num
